A common opportunistic foraminiferal species as an indicator of rapidly changing conditions in a range of environments

Long-term biological and environmental time-series (several decades to centuries) are essential for distinguishing between anthropogenically and naturally induced environmental change as well as for monitoring environmental change over time, irrespective of the causes. Since such long time-series are virtually non-existent for most areas, other methods have to be explored which can provide the best possible analogues. Numerous investigations have shown that benthic foraminifera (meiofaunal protists), which leave a fossil record in most marine sediments, are well suited for this purpose. A prerequisite for performing sound interpretations is an optimal understanding of their biology and ecology. Stainforthia fusiformis (Williamson) is one of the most common benthic foraminiferal species in NW European waters and living (stained) populations have been recorded in all clastic, soft bottom intertidal to outer shelf and slope areas with sediments consisting of at least some fines (>4% <63 lm) as long as the salinity is >28. Its predominance in ephemerally dysoxic/anoxic areas has caused it to be used as a proxy for severe oxygen depletion. A strong dominance (even >90%) of this species is, however, also reported from well-oxygenated coastal and shelf settings and, consequently, high abundance of this species occurs in habitats with very different environmental characteristics. A closer examination of these areas suggests that they can be roughly grouped into three categories: (1) beneath hydrographic frontal areas, (2) physically disturbed areas of sediment, and (3) ephemerally dysoxic/anoxic basins. The main characteristic feature that these highly different environments have in common is that they experience rapidly changing conditions. It is concluded that the opportunistic life-strategy of S. fusiformis makes it highly adapted to cope with environmental stress and that this, rather than tolerance to a particular environmental parameter, causes it to predominate in areas subject to rapidly changing environmental conditions.